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I posted last May about a custom 6sn7 preamp that was runnnig too hot and had a few cap failures. Here is an update,So after another failure due to heat(burnt resistors), I took it back to the engineer for a power supply rebuild. Redesigned power supply in a separate box with 5AR4 tube rectification. Preamp box uses 0A2 and 0B2 tube voltage regulators. Runs cool and so far so good.
Thomas
"In a democracy, uneducated voters get the leaders they deserve."
Edits: 08/02/17Follow Ups:
So I am not an engineer, and can't really read schematics. But it's still working after 50 hours. Power supply was designed by someone who does this for a living, friend of the gentleman who put it together(retired Naval Communications engineer). Confidence level is high that between the 2 of them, this thing is solid.
Thomas
"In a democracy, uneducated voters get the leaders they deserve."
First, it is drawn that the two 6.3 v secondaries are connected out of phase.
Then you have a bridge rectified 6.39 volt DC connected to a 28 volt reference on the positive end and ground on the other. This does not work and has to be drawn wrong.
You raise a DC supply by referencing the ground side to the elevated voltage.
If it was build like the drawing, you have some opportunities for improvement.
Glad you got it fixed. Love those 'SN7s!
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Buy Chinese. Bury freedom.
Is there an advantage to raising the voltage on the heater line, if it's already rectified to DC?
Thanks!
There's some rumbling about improved performance with 50-90V of bias on the heaters of indirectly heated tubes. In a tube preamp like that one, one would presume that at least one cathode is quite elevated WRTG, so biasing up the heater supply isn't an impractical precaution to take.
There's probably a cathode follower or pseudo-SRPP where the cathode-heater voltage limit might otherwise be exceeded.
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Buy Chinese. Bury freedom.
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